ABSTRACT Multi-organ dysfunction syndrome (MODS) leads to significant morbidity and mortality in critically ill patients. Acute kidney injury (AKI) is one of the most common components of MODS. Unresolved AKI leads to ongoing renal injury, fibrosis, and subsequent chronic kidney disease (CKD). However, the mechanisms that direct renal recovery and prevent the AKI to CKD transition are poorly understood. One novel and promising therapeutic approach is to modulate the functions of macrophages and dendritic cells (DCs) that accumulate in the injured kidney in order to prevent further injury and fibrosis. Interleukin (IL)-1??? are canonical pro-inflammatory cytokines that activate macrophages and DCs after binding to their cell surface receptor, IL-1R1. IL-1R1 activation plays a prominent role in renal healing. However, IL-1R1?s specific effects on macrophage and DC function following AKI and on the AKI to CKD transition are poorly understood. Based on our preliminary studies, our central hypothesis is that following AKI, macrophage IL-1R1 activation triggers TNF? (TNF)-dependent renal cell necroptosis, which directs IL-1R1-dependent migration of DCs to lymph nodes to activate pro-inflammatory T cells to drive the AKI to CKD transition. We will test our central hypothesis as follows: Specific Aim 1: Determine effects of macrophage IL-1R1 activation on TNF-mediated renal cell necroptosis following ischemic AKI. Mice with macrophage-specific deletion of IL-1R1 (IL-1R1 MKO) and controls (IL-1R1 MWT) will undergo ischemia/reperfusion (I/R)- and septic AKI, and the severity of acute kidney damage will be quantified. Renal cell necroptosis will be measured in injured kidneys and in macrophage-renal tubular cell (RTC) co-culture. We will employ cell surface phenotyping and single cell RNA-seq on sorted leukocytes from injured kidneys to precisely phenotype myeloid cells to determine how IL-1R1 activation modulates macrophage polarization and renal injury. Specific Aim 2: Elucidate the role of IL-1R1-mediated dendritic cell migration and T cell activation during the AKI to CKD transition. Mice with deletion of IL-1R1 in DCs (IL-1R1 DCKO) and controls (IL-1R1 DCWT) will be subjected to I/R-induced AKI, and at multiple timepoints, the severity of renal damage and fibrosis will be compared. We will examine IL-1R1-mediated accumulation of DC subsets in renal lymph nodes following I/R and their consequent activation of effector lymphocytes. We will use novel tissue cytometry to analyze spatial distribution of DC and T cells within fibrotic areas. Activated DC and T cells will be co-cultured with RTC to determine their effect on pro-fibrotic gene expression programs. The proposed studies will have a significant positive impact by promoting the development of future targeted treatments for patients with life-threatening AKI. Together with my training plan, these studies will lay the foundation for my development as an independent investigator in critical care medicine focused on identifying treatments that promote renal healing after AKI to prevent CKD and remote organ failure.